One important field is formed by the security inspection of luggage at travel points, such as airports. When considering luggage inspection identifying the unknown substances is especially challenging as they are always lying behind a barrier, formed by a suitcase or bag, and may even be concealed in a container. Classic examples of unknown substances that are to be identified in luggage are contraband and dangerous materials, such as explosives. One important class of unwanted substances in luggage is formed by liquid explosives. The challenge is further enlarged as in air ports time is an essential factor, putting severe constraints on the method and the device with respect to a short turnaround and a low false rate.
Summarizing in the field of luggage inspection there exists an urgent need for fast and reliable identification of unknown substances, especially explosive liquid materials that are present behind a barrier and/or concealed in a container.
The present invention aims at providing a solution to this problem with the method according to the preamble of claim 1 and the device according to the preamble of claim 7.
Such a method and device are known in the field from U.S. Pat. No. 5,428,657. The known method allows for discrimination between materials, specifically used as basis for poultry screening. Three types of material, bone, fat and poultry meat are discriminated in order to keep the poultry meat bone free. The known method uses X-ray scattering, particularly the Rayleigh scatter in forward scattered geometry under small angles and also backscattered signal such as the Compton signals or as a cross check the Rayleigh—Compton ratio. For the analysis of bone use is made of forward scattered Rayleigh signal under small angles, around 5 degrees, completely penetrated through the material.
It is noted that another method for identifying unknown substances in an object is known from EP2075570. The known method is based on X-ray Diffraction (XRD) techniques. Generally, however, XRD is a method for determining crystalline materials while identification of the class of amorphous solids and moreover liquids is today seen as not generally solved. XRD, as said, being a suitable method for the investigation of predominantly crystalline material, is normally applied for lower X-ray energies (Cu, Mo, Ag as characteristic radiation and ≦60 kV high tension or voltage) as known for materials analysis. Here in the case of luggage control higher energies and higher tensions, for example 160 kV, are applied in order to penetrate through the luggage. The useful signals are here in the forward direction under small angles so that the known method works in transmission. In order to pinpoint materials more specifically and to enter into the realm of liquids, in the known method said diffraction profiles are taken under further investigation considering still finer and smaller details. Diffraction at amorphous materials generally is not governed by intrinsic peaks compared to crystalline substances. In the end there remains the challenge of significant signal strength and feature significance and differences in features from substance to substance in order to deduce the right information.